Refrigerating system with roughened restrictor tube



July 30, 1968 R. c. ISCHWING REFRIGERATING SYSTEM WITH ROUGHENED RESTRICTOR TUBE Filed Aug. 31. 1966 Fig./

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I 3 m F United States Patent REFRIGERATIN G SYSTEM WITH ROUGHENED RESTRICTOR TUBE Richard C. Schwing, Troy, Mich., assignor to General Motors Corporation, Detroit, Mich, a corporation of Delaware Filed Aug. 31, 1966, Ser. No. 576,316 4 Claims. (Cl. 62-511) ABSTRACT OF THE DISCLOSURE In the preferred form, the refrigerating system is provided with a long open restrictor tube having its interior surfaces roughened either mechanically or chemically to minimize the effect of any rough chemical deposits upon the refrigerant flow. In addition to this, or alternately, the restrictor tube may be provided with a wire having a mechanically or chemically roughened surface.

This invention pertains to refrigerating systems in which a restrictor tube is used to control the flow of refrigerant from the condensing means to the evaporating means.

It has been discovered that frequently there are chemical deposits which accumulate in the restrictor tube of refrigerating systems. These deposits gradually roughen the surface within the restrictor tube. These deposits are greater in the portion nearest the evaporating means but they are usually not so great as to greatly reduce the cross-sectional area available for flow within the tube. However, the roughness substantially increases the friction factor thereby substantially reducing the refrigerant fiow which in turn substantially reduces the capacity of the system below that originally attainable. Efforts to reduce the tendency to cause the deposits have not been fruitful but it has been discovered that some types of refrigerants (viz CHCIF CHCl F) deposit at a greater rate than others (viz CCl F CClF CCLF It is an object of this invention to provide a restrictor tube with a simple inexpensive means which will prevent deposits within the tube from substantially reducing the refrigerant flow.

It is another object of this invention to provide a restrictor tube with a roughened interior surface sufficient to prevent any substantial reduction in refrigerant flow upon accumulation of chemical deposits.

These and other objects are attained in the form shown in the drawing in which the refrigerating system is provided with a long restrictor tube having its interior roughened either mechanically or chemically to minimize the effect of any such deposits upon the refrigerant flow. In addition to this, or alternatively, the restrictor tube may be provided with a wire having a mechanically or chemically roughened surface. The roughness may also be provided by a wire coiled within the restrictor tube.

Further objects and advantages of the present invention will be apparent from the following description, reference being bad to the accompanying drawing, wherein a preferred embodiment of the present invention is clearly shown.

In the drawing:

FIGURE 1 is a diagrammatic view of the refrigerating system illustrating one form of my invention;

FIGURE 2 is an enlarged sectional view of a portion of the restrictor tube shown in FIGURE 1; and

FIGURE 3 is an enlarged sectional view of a portion of a modified restrictor tube.

Referring now to the drawing, there is illustrated in FIGURE 1 a condenser 20 forming a first heat transfer means, an evaporator 22 forming a second heat transfer means and a sealed motor compressor unit 25 which withdraws evaporated refrigerant from the evaporator 22 through the suction conduit 24 and compresses this refrigerant and discharges the compressed refrigerant through the discharge conduit 26 into the condenser 20. The sealed motor compressor unit 25 is supplied with electric energy through the supply conductors 28 under the control of a suitable switch 30.

To assure condensation of the refrigerant in the condenser 20 and the evaporation of the refrigerant in the evaporator 22 there is connected to the outlet 32 at the bottom of the condenser 20 a restrictor tube 34 which may have an intermediate portion 36 located in heat transfer relation with the suction conduit 24 to provide a desirable transfer of heat. The opposite end of the restrictor tube 34 connects to the inlet 38 at the bottom of the evaporator 22. Restrictor tubes generally have been used between the outlet of the condenser and the inlet of the evaporator for many years. These tubes have been provided with as smooth an interior surface as is possible in the customary methods of manufacturing of such tubing. It has been discovered by many researchers in the field that when some refrigerants (such as CHClF are used there is a chemical deposit of material within the restrictor tube which is greater adjacent the inlet 38, for example, of the evaporator 22. A number of other refrigerants also deposit such materials. Primarily, it is not the reduction in the cross-sectional area for flow within the tubing but the roughness of these deposits which introduces substantially increased friction to the flow of the refrigerant thereby restricting the flow of refrigerant substantially below the flow for which the restrictor tube was originally designed. This reduces the capacity of the system so that it is unable to carry the refrigerant load for which it was originally designed.

According to my invention, to prevent this substantial reduction in flow and this substantial reduction in refrigerating capacity, I provide the entire interior of the restrictor tube 34 with a roughened surface 40. Preferably this surface 40 is roughened to the maximum extent that is economically obtainable either by mechanical or chemical roughening. The roughened surface imposes a greater friction to the flow of the refrigerant so that this must be compensated for by either shortening the length of the restrictor tube or by increasing its inside diameter. As a result of this toughening, when the deposition takes place upon the interior surface of the restrictor tube there is substantially no increase in the roughness of the surface and very little increase in the friction so that there is substantially no reduction in refrigerant flow. The physical form of the deposits is so small in proportion to the cross-sectional area that the deposits do not substantially restrict the free cross-sectional area for flow within the tube so that the refrigerating system is substantially unaffected by the deposits.

In addition to this, or as an alternative, the restrictor tube 34 may be provided in its interior with a wire 42 having a similarly roughened surface 44 throughout. The wire 42 presents a sufiicient area of roughened surface so that the deposit does not substantially change the frictional flow characteristics of the restrictor tube so that the performance of the system is not substantially reduced.

A modified form of the invention is shown in FIGURE 3. In this modified form the substantial reduction in refrigerant flow is prevented by inserting within the capillary restrictor tube 34 a very small diameter helically coiled wire 48 which substantially fits against the inner wall surface of the tube 34. If desired, this wire 48 as well as the interior wall surface of the tube 34 may also be mechanically or chemically roughened. However, this is not necessary. In this form, the presence of the coiled wire 48 within the tube 34 causes a sufficient increase in the frictional resistance to the flow of the refrigerant through the tube 34 that there is substantially little or no increase in the friction when the deposition of the particles takes place within the interior of the tube 34. Therefore, the flow within the tube and the capacity of the refrigerating system will be substantially unaffected by the deposits. The coiled wire 48 within the tube 34 will impose a greater frictional resistance to the flow of refrigerant which is compensated for by shortening the length of the tube 34 or increasing its diameter to provide the capacity for refrigerant fiow.

While the embodiment of the invention as herein disclosed constitutes a preferred form, it is to be understood that other forms might be adopted.

What is claimed is as follows:

1. A refrigerating system including a first heat transfer means adapted to contain a refrigerant, a second heat transfer means adapted to contain the refrigerant, a compressor means for withdrawing evaporated refrigerant from the second heat transfer means and discharging the compressed refrigerant into the first heat transfer means to establish a lower pressure in the second heat transfer means and a higher pressure in the first heat transfer means, a long open small bore resistor tube means connecting said first and second heat transfer means for controlling the How of refrigerant from the first to the second heat transfer means and in operation establishing a selected restriction to refrigerant flow sufiicient to establish a range of difference in pressures between said first and second heat transfer means associated with the operation of the compressor means, the flow of refrigerant through the restrictor tube means being characterized by the build up over a prolonged period of operation of fiow restricting rough deposits therein, the restrictor tube means in its initial form having roughened interior surfaces such as to create an initial roughness providin an initial restriction to refrigerant flow substantially equal to the restriction to refrigerant fiow characteristic of the restrictor tube means after said flow restricting rough deposits have accumulated.

2. A refrigerating system including a first heat transfer means adapted to contain a refrigerant, a second heat transfer means adapted to contain the refrigerant, a compressor means for withdrawing evaporated refrigerant from the second heat transfer means and discharging the compressed refrigerant into the first heat transfer means to establish a lower pressure in the second heat transfer means and a higher pressure in the first heat transfer means, a long open small bore restrictor tube means connecting said first and second heat transfer means for controlling the flow of refrigerant from the first to the second heat transfer means and in operation establishing a selected restriction to refrigerant flow sufficient to establish a range of difference in pressures between said first and second heat transfer means associated with the operation of the compressor means, the flow of refrigerant through the restrictor tube means being characterized by the build up over a prolonged period of operation of flow restricting rough deposits therein, the restrictor tube means in its initial form having mechanically roughened interior surfaces such as to create an initial roughness providing an initial restriction to refrigerant flow substantially equal to the restriction to refrigerant flow characteristic of the restrictor tube means after said flow restricting rough deposits have accumulated.

3. A refrigerating system including a first heat transfer means adapted to contain a refrigerant, a second heat transfer means adapted to contain the refrigerant, a compressor means for withdrawing evaporated refrigerant from the second heat transfer means and discharging the compressed refrigerant into the first heat transfer means to establish a lower pressure in the second heat transfer means and a higher pressure in the first heat transfer means, a long open small bore restrictor tube means connecting said first and second heat transfer means for controlling the fiow of refrigerant from the first to the second heat transfer means and in operation establishing a selected restriction to refrigerant flow sufiicient to establish a range of difference in pressures between said first and second heat transfer means associated with the operation of the compressor means, the flow of refrigerant through the restrictor tube means being characterized by the build up over a prolonged period of operation of flow restricting rough deposits therein, the restrictor tube means in its initial form having chemically roughened interior surfaces such as to create an initial roughness providing an initial restriction to refrigerant flow substantially equal to the restriction to refrigerant flow characteristic of the restrictor tube means after said flow restricting rough deposits have accumulated.

4. A refrigerating system including a first heat transfer means adapted to contain a refrigerant, a second transfer means adapted to contain the refrigerant, a compressor means for withdrawing evaporated refrigerant from the second heat transfer means and discharging the compressed refrigerant into the first heat transfer means to establish a lower pressure in the second heat transfer means and a higher pressure in the first heat transfer means, a long open small bore restrictor tube means connecting said first and second heat transfer means for controlling the flow of refrigerant from the first to the second heat transfer means and in operation establishing a selected restriction to refrigerant flow sufi'icient to establish a range of difference in pressures between said first and second heat transfer means associated with the operation of the compressor means, the flow of refrigerant through the restrictor tube means being characterized by the build up over a prolonged period of operation of flow restricting rough deposits therein, and a wire having a roughened exterior surface such as to create an initial restriction to refrigerant fiow substantially equal to the restriction to refrigerant flow characteristic of said restrictor tube means after said flow restricting rough dcposits have accumulated.

References Cited UNITED STATES PATENTS 2,166,109 7/1939 Karmazin 62-5l1 XR 2,418,671 4/ 1947 Schwellcr 62-51l XR 2,576,610 11/1951 Kunzog 62--511 XR 2,604,119 7/1952 Hughes 6251l XR MEYER PERLIN, Primary Examiner. 

